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It sounds as though you have a reasonable grasp of the process. The one thing I'd recommend is a layer of woven fibreglass, as foam, chopped strand matting, and gelcoat don't have much structural strength. I prefer microballoons to Cabosil, but to each their own.

You may want to consider using polyester resin rather than epoxy. Polyester is what your Whaler was originally built with - it is less fussy to work with than epoxy, and compatible with gelcoat. Epoxy is not, so you'll need to do something to get the gelcoat to adhere properly to it.

Tim